He told BANG Showbiz: "It was important that each character came alive, so we were looking for actors with great vocals and the ability to act with their voices.

"A lot of actor's skills lay in their visuals so it's always more important to have a compelling voice rather than a big name."

Disney have been playing with the idea of a film based on 'The Snow Queen' fairytale since Walt Disney himself was still alive, and although the writers of 'Frozen' decided on two female characters, it wasn't until someone suggested they be sisters that the story really took shape.

Co-director Jennifer Lee explained: "That was really the moment. We keep saying, 'Was it you? No, it was you...' because we don't remember, but the whole story just felt more special to everyone. Everyone could relate to that."

Jennifer's fellow director, Chris Buck, added: "There was a connection. Especially with these two characters, when you split them apart, because they were siblings, suddenly all you're doing for the rest of the movie is rooting for them to get back together."

Princess Anna (Bell) is disturbed to find that her sister Elsa (Menzel) can create ice and snow, but when Elsa goes into exile the kingdom freezes, and Anna and friends must find her. With no celebrity voice-overs or pop culture gags, just a venerable story, good songs and classic characters, it's an old-fashioned delight.